Traditional circuit breakers employ electro-mechanical means to provide protection against current overload and inrush. Similarly, circuit breakers employing electronic circuits to detect and trip the breakers when ground faults and/or arc faults are detected also generally incorporate an electro-mechanical means to provide protection against current overload and inrush. In these circuit breakers the electronics generally do not provide monitoring or protective control of the breaker in regard to current overload or inrush. Thus, should the electronic circuitry protecting against ground fault and/or arc fault fail, the breaker will still maintain its protection against overload and excessive inrush current.
Ideally, such a circuit breaker would also be able to employ electronic circuitry, either solely or combined with ground-fault and/or arc fault protection, to monitor current overload and inrush current and thereby trip the breaker should either be excessive. The electronics therein would be able to be exactingly programmed to provide precise protection against overload and inrush current. The problem with only employing electronic circuitry to provide a breaker's protective capability has been that, should the electronic circuitry fail, the breaker could remain in an “on” (connected) status during an overload, resulting in a dangerous, unacceptable condition.
An electro-mechanical circuit breaker that employs either thermal bi-metal construction, or hydraulic-magnetic construction, to provide current overload and inrush protection, is not completely failure proof, but is designed to be as failure proof as possible. Thus, any design of an electronically controlled circuit breaker would necessitate a similar degree of failure proof construction as inherent within traditional electro-mechanical circuit breaker designs.
Safety becomes a major factor in any employment of electronic circuit breakers that rely totally on solid-state microprocessor controlled electronics to provide protection without the incorporation of a physical contact opening during a trip (i.e., off) state. Also, existing technology for circuit protection that solely employs solid-state microprocessor controlled electronics to switch high voltage power incurs high cost and significant heat dissipation problems. The most practical and safe approach is to combine microprocessor based electronics to monitor the desired circuit protection parameters with a mechanical contact mechanism that would provide a physical contact gap in the open (i.e., off) position.
Historical attempts have been made to provide electronic circuit breakers that rely totally on solid-state microprocessor controlled electronics to provide protection against current overload and inrush current in addition to ground-fault and/or arc fault protection. However, none of these historical attempts has resulted in a circuit breaker design that provides a similar degree of failure proof construction as inherent within traditional electro-mechanical circuit breaker designs.
For example, U.S. Pat. No. 4,331,999 to Engel et al. and U.S. Pat. No. 4,338,647 to Wilson et al. disclose circuit interrupters with a digital control unit (154) that causes tripping of a trip coil (22) in response to various sensed conditions. However, both references discuss the use of a switching field effect transistor (192) to control the flow of current through the trip coil (22) in response to signals from the digital control unit (154). As such, in the case of failure within the digital control unit (154) and/or the transistor (192), the transistor (192) may be stuck in the unenergized state, thereby rendering the trip coil (22) inoperative, resulting in a potentially dangerous condition.
As such, there remained an unmet need in the industry for an electronically controlled circuit breaker that incorporates a mechanical contact mechanism while maximizing the fail-safe level of the breaker to insure its ability to provide the required circuit protection.
Many of these concerns have been addressed in my currently co-pending U.S. patent application Ser. Nos. 15/959,882 and 16/113,534, both entitled “Electronic Circuit Breaker With Physical Open-Contact Construction and Fail Safe Protection.”
In order to remedy the deficiencies of previous designs, these applications disclose various embodiments of a circuit breaker that includes a normally closed relay having a relay activating circuit and a switching circuit, with the switching circuit being electrically connected to a trip coil. A monitoring circuit is electrically connected to the relay activating circuit, supplying activating power to the relay activating circuit so long as a determination is made that the breaker is operating within acceptable parameters, and ceasing to supply activating power to the relay activating circuit upon a determination being made that the breaker is not operating within acceptable parameters, thereby tripping the breaker.
However, one issue not specifically addressed in these applications relates to situations where the trip coil and/or the electronic monitoring circuit might become damaged, for example, in the case of an extremely high voltage surge. In these types of situations, it is conceivable that the damage may prevent proper functioning of the breaker (i.e., opening of the contacts), and consequently, it is possible for power to unintentionally be allowed to flow through the breaker if the breaker is reset. However, power flowing through a damaged circuit breaker may be problematic, and indeed potentially catastrophic. It would thus be desirable for a damaged circuit breaker to be permanently disabled such that power could not unintentionally flow therethrough regardless of how many attempts may be made to reset the breaker.